#29775 ghostty-next: the wrap edge break reads a compressed history row only when the pair was joined

Summary

• Follow-up to #29609, from its review note 1. In ghostty-next, Screen.breakWrapAbove read the row above before it checked the flags. So IL or DL at the screen's top row restored the last history page from compression on every call. Under load, a region scroll can run once per output line.
• The fix is fork PR manaflow-ai/ghostty-next#68. The function now decides on the resident row first (its wrap_continuation, or for IL/DL the top row's flag read before the rows move). It reads a row in a compressed history page only when the pair was joined.
• The pin moves to GhosttyNextKit xcframework-84a225487372c53851b186864c867e469e7596d2-apple-v6, on release/cmux-9ce9b7d0-e2. That release is 8444cc1eb (the #29609 pin) plus only #68. The gitlink, package-notices.json and vt-link-graph.json move with the pin.
• Review note 2: every commit ID in the E2 section of docs/ghostty-fork.md is now a release-branch ID, and the section says so.

Testing

• Red: fork run 41240560795. The new Zig test "insertLines and deleteLines at the top row leave a compressed history page compressed" fails without the fix.
• Green: fork PR #68 run 41240575661, and the release run 41241826620, which built and published this kit.
• The cmux Rust replay tests on this pin: see the fleet step in a comment below.

Observed / Not run

• Observed: the red and green fork runs above. SHA256SUMS of the release lists 66e883f7130352862fd3dd4b46cf0a6d22d50750bf633f3589831bf9b2f4f99f, which is the checksum in Package.swift.
• Not run: a timing benchmark. The test proves that the common case leaves the compressed page alone. It does not measure time.

Changelog

none

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Summary by cubic

Fixes a performance issue in ghostty-next where Screen.breakWrapAbove read a compressed history row before checking flags, so IL or DL at the screen's top row restored the last history page from compression on every call. The function now decides on the resident row first and reads a compressed row only when the pair was joined.

• Pins GhosttyNextKit xcframework-84a225487372c53851b186864c867e469e7596d2-apple-v6 (checksum 66e883f7...); the gitlink, package-notices.json, and vt-link-graph.json move with it.
• Adds the Zig test "insertLines and deleteLines at the top row leave a compressed history page compressed", which fails without the fix and passes with it.
• docs/ghostty-fork.md now states that every commit ID in the E2 section is a release-branch ID.